Solution : https://service.sap.com/sap/support/notes/333649 (SAP Service marketplace login required)
Key words : 
debit position0170538 performance improvements service charge settlement0318388 sequential reading, creating fi documents313247 -> fi performance problem whn processng, tax calculation0328629 performance service charge settl, billng due list209207 -> fi performnce problm, 6b upgrade0333323 performance problem, financal accountng204325 -> fi perform, entries170989 views perform poorly, prerequisites performance problems occur, additional key words slow, performance problems monitored
Related Notes : 
       
| 359907 | Buffering RF_BELEG/number assignment in FI | 
| 315202 | Error in NUMBER_GET_NEXT | 
| 199441 | Performance problems for RE | 
| 179224 | Doc.no.assignment for unbuffered number ranges | 
| 142237 | Process waits infinitely for number range buffers |